The present invention relates to a link actuating device to be utilized in a link mechanism, such as a robot joint, for quickly and accurately executing an operation in a three-dimensional space, such as a complicated machining or article handling.
For example, as a link actuating device for quickly and accurately executing an operation in a three-dimensional space, such as a complicated machining or article handling, there exists an operation device equipped with a parallel link mechanism (see, for example, JP 2000-94245 A).
This operating device is equipped with a parallel link mechanism in which a plurality of links connecting a base plate and a traveling plate are caused to expand and contract in cooperation with each other, thereby varying the position and attitude of the traveling plate with respect to the base plate. By mounting a tool to the traveling plate of this parallel link mechanism and rotatably arranging a table retaining a workpiece, it is possible to freely change the position and attitude of the tool with respect to the workpiece on the table, thereby making it possible to perform a complicated machining, article handling, etc. in a three-dimensional space by the tool.
The above-mentioned parallel link mechanism has superb features for quickly and accurately executing an operation in a three-dimensional space, such as a complicated machining or article handling; for example, it allows a reduction in the mass of the movable portions, and the positioning errors of the links are made uniform in the forward end portions thereof.
However, in the above-described parallel link mechanism, the operation angle of each link is rather small, so that an attempt to set the operation range for the traveling plate large results in a rather large link length, which leads to an increase in the size of the mechanism as a whole, resulting in an increase in the device size. Further, the rigidity of the mechanism as a whole is rather low, so that there is a limitation regarding the weight of the tool that can be mounted on the traveling plate, that is, the weight capacity of the traveling plate.
To solve the problem described above, the present applicant has proposed a link actuating device equipped with a link mechanism which is of a compact construction and of high rigidity and which exhibits a large weight capacity (JP 2004-261886 A).
This link actuating device has three or more sets of link mechanisms in each of which end link members are rotatably connected to link hubs respectively provided on an input member and an output member, with the input side and output side end link members being rotatably connected to an intermediate link member, the input side and the output side being geometrically the same with respect to a cross section at the central portion of each link mechanism. Each link mechanism constitutes a three-junction chain composed of four rotation pair portions.
In this link actuating device, bearing outer rings are contained in the link hubs, and bearing inner rings are connected with the end link members to thereby embed bearing structures in the link hubs, in which a rotation transmission portion is arranged in the inner space of each of the link mechanisms, and there are provided actuators for controlling the attitude of the end link members through the rotation transmission portions; by fixing the input side link hub and driving the rotation transmission portions, the output side link hub is operated through 2 degrees of freedom.
In this link actuating device, the rotation pair portions of the link mechanisms adopt a cantilever support structure, so it is hardly to say that the link mechanisms are superior in terms of strength. Therefore, the rigidity of the link mechanisms is rather low. Further, in the rotation pair portions of the link mechanisms, grooves are formed in the link hubs, and snap rings are fit-engaged with the grooves, thereby preventing detachment of the bearings.
However, in a bearing detachment prevention structure for the rotation pair portions of a link mechanism utilizing a snap ring, there is involved an axial gap between the snap ring and the groove with which it is fit-engaged, and movement in the axial direction of the rotation pair portions is possible by an amount corresponding to this gap, resulting in rattling of the link mechanism. Further, to fill up a radial gap, it is necessary to press-fit the bearing outer ring into the link hub, so that, once assembled, the mechanism is rather difficult to dismantle. As a detachment prevention means other than the snap ring mentioned above, crimping may be adopted; in this case, however, dismantling is impossible, and no reproduction is allowed, so that sufficient care is needed in assembling, and a problem in terms of maintenance performance is also involved.
Further, in this link actuating device, for its link mechanisms to operate in a wide range without involving any interference between the components forming the link mechanisms, an appropriate contrivance is needed regarding the configuration of the components forming the link mechanisms. Further, it is also necessary for the components to be configured taking into account the assembly property and workability of the link mechanisms.